Coordination of limb movements requires continuous interactions between cortical neurons in separate regions representing different components of the movements. We tested the hypothesis that intracortical interactions may be mediated by temporal synchrony between the firing of neurons, as reflected in synchronization of field potentials. We documented the activity of arm-related neurons in left and right motor cortical areas in two macaques performing a coordinated bimanual tracking task. The monkeys controlled the two-dimensional position of a cursor on a video screen by operating two joysticks separately with the left and right hand. Each joystick controlled one axis of the cursor position (x or y position). Both monkeys performed well in tracking a randomly moving target. Simultaneous neuronal and local field potential recordings were obtained from movable microelectrodes in left and right primary motor cortex (M1); chronically implanted electrodes also recorded fiel d potentials at symmetric sites in supplementary motor cortex (SMA) and parietal cortex (area 7). Field potentials in M1 and SMA showed oscillations at 10-15 Hz (monkey 1) or 20-30 Hz (monkey 2) that could become bilaterally synchronous during the bimanual movements. In the absence of bimanual movements the right and left M1 fields were not synchronized. Field potentials in parietal cortex showed oscillations that could become synchronized with M1 and SMA at the same frequency, but could also show bilateral synchrony independently of the bilateral synchrony of M1 and SMA. These results indicate that bimanual coordination is accompanied by interhemispheric synchronization of activity in motor cortical areas. These data are being analyzed further to investigate the relationsbetween synchronous episodes and specific components of the bimanual movements. FUNDING RR00166 and NS12542. Perlmutter, S., Maier, M., and Fetz, E.E. Activity and output linkages of spinal premotor interneurons during voluntary wrist movements in the monkey. J. Neurophysiol. 80 2475- 2494, 1998. Maier, M., Perlmutter, S. and Fetz, E.E. Response patterns and force relations of monkey spinal interneurons during active wrist movement. J. Neurophysiol. 80 2495-2530, 1998. Fetz, E.E., Smith, W., Prut, Y., Maier, M. and Perlmutter, S.I. Neuronal interactions in primate sensorimotor cortex and spinal cord during voluntary movements. Eur. J. Neurosci. 10 433, 1998 Prut, Y., Perlmutter, S.I. and Fetz, E.E. Activity of spinal interneurons during premovement delay period in primates. Soc. Neurosci. Abstr. 24 918, 1998. Kawashima, T., Knight, T.A. and Fetz, E.E. Interhemispheric synchronization of neuronal and field potential activity during bimanual movements of monkeys. Soc. Neurosci. Abstr. 24 403, 1998. Fetz, E.E. Dynamic activities in neuronal populations of primate sensorimotor cortex. Proc. Third Riken-Tamagawa International Dynamic Brain Forum., p. 8, 1998.